This invention relates generally to vacuum film holders and more particularly to an arrangement for properly locating the registration pins on a film holding device of the type used in film projection.
In the projection of film images onto an easel, vacuum film holders equipped with registration pins serve to hold the film at precisely the correct location for proper projection. The film holder includes a metal frame and a glass pane which fits in a rectangular opening formed through the frame. The glass pane rests on a recessed shelf or ledge that extends around the frame opening. A thin vacuum channel is formed between the frame and the edge of the glass in order to apply vacuum to the film for holding it flatly against the glass.
Registration pins are of use when successive, congruent images must be individually and separately positioned and exposed to a common sensitive medium so that they become a composite. When unpunched film is passed over the same film holder and vacuumized, the pins cannot be present. Thus it is essential that the pins be made easily and quickly removable and/or replaceable. The present invention provides for this capability.
For economy reasons and to achieve the best possible quality in the finished print, film images are made to cover the greatest possible area on a given piece of film. This means that the space between the edge of the image and the edge of the film is made as narrow as possible even though this area is required to fall over the vacuum channel. The reason is that when in the projection mode, the vacuum channel cannot underlie the image area, lest it show in the finished picture.
Further economies can be achieved if the pins and the film punch holes can be located more or less centering them over the vacuum channel, but this creates a nearly insurmountable difficulty because the pins then block the vacuum channels, preventing the passage and egress of air out through the channels with resultant vacuumizing of the film.
This invention satisfies all the requirements, namely, using pins which can be precisely positioned to match the punched holes in the film, easily installed and easily and quickly removed and configured to obviate blocking the passage of air.
Registration pins are often needed at opposite ends of the frame to interfit with punched film in a manner to maintain the film at the proper location for projection of the film image and to relate successive, preregistered films with respect to the film holder (and the optical axis) in the same attitude. The registration pins are necessary at some times and are not used at other times. When the pins are required, they do not interfere with the film holding function of the device. However, the center to center dimension between the registration pins is sometimes designated and can cause problems if the vacuum channel-to-vacuum channel distance is about the same as the pin-to-pin distance.
For example, on film holders which have a nominal 8 inch image size, current standards call on occasion for a 9 inch center to center dimension between the registration pins. Due to the need for a shelf of about 1/4 inch on each end of the holding frame for the glass pane in order to support the glass, the frame opening must be 81/2 inches long for a nominal 8 inch aperture size. Adding another 1/4 inch at each end for the glass results in coincidence between the registration pins and the vacuum channel. When holes for receiving the pins must be drilled in the frame at locations where they tend to break out into the space of the vacuum channel, the situation is unacceptable from a fabrication standpoint. These problems, coupled with the need to alternately provide and remove the registration pins, have not been successfully dealt with by the industry prior to the present invention.